Apparatus for reacting a gas and a particulate material in an enclosure, and method for operating said apparatus

Abstract

The reactor includes: a lower zone (I) having a fast circulation fluidized bed; a zone having a dense fluidized bed (13) and located adjacent to the top of the lower zone, being separated therefrom by a dividing wall, the top layer of the dense bed receiving falling particulate materials, and its bottom layer returning these materials to the lower zone (I); and a higher zone having a fast circulation fluidized bed. The invention is applicable to boilers.

We claim: 
     
       1. In an apparatus for performing an exothermal or an endothermal reaction comprising a reactor including an enclosure having a wall, a top and a bottom, said reaction being between at least one gas and at least one particulate material and said apparatus further comprising at least one means for introducing particulate material and at least one means for introducing fluidization gas into said reactor enclosure having respective introduced flow rates of said particulate material and said fluidization gas with said gas velocity being higher than the velocity of the particulate material, 4 to 12 m/sec thereby establishing a fast upward flow of gas and particulate material inside the reactor enclosure and defining a fast fluidized bed, means for directing a mixture of the reaction gas and the particulate material reaching the top of the reactor enclosure into a separator, means for exhausting the gas produced by the reactor, and means for recycling the particulate material from the separator to the bottom of the reactor enclosure, and wherein the reactor comprises: a) a lower zone (I) having a top and a bottom comprising a fast fluidized bed F 1  with a mean upward gas velocity V 1  under empty conditions and at full load in a range of 4.8 m/s to 12 m/s and said fluidized bed F 1  having a height such that a gas residence time through said lower zone (I) lies in a range of 0.25 seconds to 4 seconds;   b) a higher zone (II) having a top and a bottom and being above said lower zone (I) and of a cross section S 2  ;   c) mean for flowing an additional fluidization gas upwards within said enclosure with a velocity in the range of 0.3 m/s to 2.5 m/s under empty conditions and at full load, defining a dense fluidized bed adjacent to the top of said lower zone (I) and being laterally separated therefrom and being disposed adjacent to at least a part of said wall of said reactor enclosure and receiving both particulate material coming upwards from the top of the lower zone, adjacent thereto, and particulate material falling down from said higher zone (I) along said part of said wall thereof; and   (d) at least one means for reinjecting particulate material from said dense fluidized bed, at a dense fluidized bed zone, to the bottom of said lower zone (I); the improvement comprising: said higher zone (II) comprising a fast fluidized bed F 2  with an upward gas velocity V 2  of the fluidization gas under empty conditions and at full load being in a range of 4 m/s to 10 m/s, and having a ratio of said upward velocity V 2  to the velocity V 1  of the fluidization gas of fluidized bed F 1  in said lower zone being in a range of 1/2 to 1/1.2, and said fluidized bed F 2  having a height of said higher zone (II) such that a residence time of the fluidization gas in said higher zone (II), at full load, lies in a range of 2 seconds to 10 seconds, and having a concentration P at the top of the higher zone (II) of the reactor enclosure of not less than 2 kg/m 3  ; and wherein a reinjection rate of said means for reinjecting particulate material from the dense fluidized bed zone is greater than the quantity   q=P×V.sub.2 ×S.sub.2,     and wherein a ratio (S 2  /S 1 ) of said cross section S 2  to a cross section S 1  of the lower zone (I) at a level of the dense fluidized bed zone (13) lies in a range of 1.20 to 2.     
     
     
       2. Apparatus according to claim 1, wherein a plurality of dense fluidized beds are disposed substantially at a same level within said reactor, and angularly distributed around a central space of said enclosure. 
     
     
       3. Apparatus according to claim 1, further including heat exchange members in said dense fluidized bed zone for exchanging heat. 
     
     
       4. Apparatus according to claim 3, further including means for adjusting a temperature of the reactor by controlling fluidization velocity of said dense fluidized bed. 
     
     
       5. Apparatus according to claim 1, further including, in said wall of the reactor higher zone (II) proximate to said fast fluidized bed therein, means for exchanging heat. 
     
     
       6. Apparatus according to claim 1, wherein said means for introducing fluidization gas comprises at least one first nozzle for injecting said fluidization gas beneath a grid beneath said lower zone (I) and second nozzles for injecting said fluidization gas at different levels of said lower zone (I). 
     
     
       7. A method of performing an exothermal or an endothermal reaction inside a reactor between at least one reaction gas and at least one particulate material, the reactor comprising an enclosure having a wall, a top and a bottom, at least one means for introducing particulate material into the bottom of the reactor enclosure, at least one means for introducing a fluidization gas into the reactor enclosure at respective introduced flow rates of said particulate material and of said fluidization gas to establish a fast upward flow of gas and particulate material inside the reactor, means for directing a mixture of the fluidization gas and the particulate material reaching the top of the reactor enclosure into a separator, means for exhausting the gas produced by the reactor, and means for recycling the particulate material from the separator to the bottom of the reactor enclosure, said method comprising the following steps: a) establishing in a lower zone (I) of the reactor a fast fluidized bed F 1  with a mean upward velocity V 1  of the fluidization gas under empty conditions and at full load in a range of 4.8 m/s to 12 m/s, and with a fluidized bed F 1  height of said zone such that a gas residence time through said lower zone lies in the range of 0.25 seconds to 4 seconds;   b) establishing in a higher zone (II) of a section S 2 , a fast fluidized bed F 2 , with an upward velocity V 2  of the fluidization gas under empty conditions and at full load in a range of 4 m/s to 10 m/s, with a ratio of said velocity V 2  of said fluidization gas in the higher zone (II) to the velocity V 1  of the fluidization gas in said lower zone (I) being in a range of 1/2 to 1/1.2, with a height of said fluidized bed F 2  being such that a gas residence time of said higher zone (II) at full load lies in a range of 2 seconds to 10 seconds, and wherein a concentration P at a top of the higher zone (II) of the reactor is not less than 2 kg/m 3  ; and   c) establishing in a dense fluidized bed zone, adjacent to a top of said lower zone (I), and separate therefrom, with a dense fluidized bed having an additional fluidization gas thereof flowing upwards at a velocity in a range of 0.3 m/s to 2.5 m/s under empty conditions and at full load, and with said zone being disposed adjacent to at least a part of said enclosure wall so as to receive both particulate material coming upwards from the top of said lower zone (I), adjacent thereto, and particulate material falling down from said higher zone (II) along at least said part of said enclosure wall; and   d) reinjecting particulate material from said dense fluidized bed zone (13) to a bottom of said lower zone (I) at a reinjection rate which is greater than the quantity:   q=P×V.sub.2 ×S.sub.2.